Cerebellar Purkinje cells of many species show a similar chemosensitivity to putative neurotransmitters. Mutations which alter cerebellar connectivity in mice similarly do not change this chemosensitivity. This work suggests that postsynaptic receptivity of the Purkinje neuron develops intrinsically and early in phylogeny. BIBLIOGRAPHIC REFERENCE: Siggins, G. R., Henriksen, S. J. and Landis, S. C.: Electrophysiology of Purkinje neurons in the weaver mouse: iontophoresis of neurotransmitters and cyclic nucleotides, and stimulation of the nucleus coeruleus. Brain Res., 114: 53-69, 1976.